Moraxella (Branhamella) catarrhalis is one of the major bacterial pathogens causing otitis media in children (Bibliography entries 1,2,3,4). It also causes sinusitis, laryngitis, tracheitis, pneumonia, and other respiratory diseases in children and adults (5,6,7). A prophylactic vaccine is clearly needed because nearly all clinical isolates are resistant to E-lactam antibiotics (8,9).
The outer membrane proteins (OMPs) of M. catarrhalis are being investigated as potential vaccine candidates because they are readily accessible to antibodies. Indeed, antibodies elicited in mice towards certain OMP's including UspA and the CopB have already been shown to have biological activity, such as bactericidal activity, adhesion blocking activity and enhanced pulmonary clearance of the bacteria in an animal model (10,11,12,13). Serology data from humans who have suffered a recent M. catarrhalis infection indicates that humans develop antibodies towards OMP's following natural infection (14,15,16,17,18). This suggests that OMP's are the targets of the host's defense mechanisms. UspA-specific antibodies are present in normal human serum and these antibodies have bactericidal activity. There are also high levels of antibodies towards OMPs of approximately 80 kD in sera from both healthy humans and patients recovering from recent M. catarrhalis infections (16). Several proteins from M. catarrhalis migrate within this size range. Among them are CopB (12), the B1 protein (18), a transferrin binding protein (TbpB) and a lactoferrin binding protein (LbpB)(19). Whether these proteins are the same or different from one another has yet to be determined. None of them, however, has been evaluated in a purified form for vaccine use.
An efficacious vaccine to protect against diseases caused by M. catarrhalis should confer protection at all stages of disease. These stages include bacterial colonization on mucosal surfaces, bacterial multiplication, spread and invasion, and the development of inflammatory response. Multiple bacterial components may be required to formulate an efficacious vaccine. Although there is pre-clinical data to suggest that some surface components of M. catarrhalis are potential vaccine antigens, it is as yet unclear if these components will confer sufficient protective immunity in humans. Thus, it is important to identify and evaluate new bacterial antigens for vaccine use.